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How much storage does your current plan allow?

How much storage do you need?

That's the amount of storage on your phone itself. The message you are seeing is your iCloud Storage. Apple gives you 5GB of free iCloud storage. For most of us, at some point that just isn't enough, so we buy more iCloud Storage, which apparently you'll need to do. For as little as $1.99/month you can buy a 50GB plan, which would be a good next step plan for you.

See how to do that here --> Upgrade to iCloud+ - Apple Support (CA)

Where exactly are you seeing this? A very common scam lately is to send such a message or email. The link takes you to a site that looks like Apple's, but entering your Apple ID and password, and/or your credit card info is really going to crooks.

Where does the link on that message go?

I made a mistake about the cost. The 50GB iCloud Storage plan is only 99 cents/month. That is only $12/year, which is very reasonable.

Open the Settings App on your iPhone.

Tap your name at the top

Tap iCloud

At the top you'll see how much storage you have available

Since it's the Photos app itself producing the message, then you can assume it's real and correct.